What is the pH of a saturated solution of Zn(OH)2? Ksp = 1.8 × 10−14?

1 Answer

• Zn(OH)2 ==⇒ Zn2+ + 2OH-

  Let s be the molar solubility of Zn(OH)2.

  The equilibrium concentrations of the ions are:

  [Zn2+] = s and [OH−] = 2s

  Ksp = [Zn2+][OH−]^2 = 1.8 x 10^-14

  (s)(2s)^ = 1.8 x 10^-14

  4s3 = 1.8 × 10^−14

  s^3 = 4.5 x 10^-14

  s = 1.65 x 10^-5

  [OH-] = 2(1.65 x 10^-5) = 3.3 x 10^-5

  pOH = -log(3.3 x 10^-5) = -(-4.48)

  pH + pOH = 14.00

  pH = 14.0 – 4.48 = 9.52